The design of hybrid integrated linear transistor microwave power amplifiers for high power, wide bandwidth and large dynamic range can be most successfully achieved through the use of a Class A operated linear amplifier. The use of Class C type amplifiers while offering high power and good efficiency are rather limited in bandwidth and in dynamic range.
In the linear broadband power amplifier the continued objective is a suitable circuit that can produce the required stable gain and power simultaneously with good power output and efficiency. Unfortunately, there exists no uniform circuit model in the microwave region that can meet all these requirements.
Commercially available transistors can be used in the design of a transistor amplifier circuit for wideband operation in the 1-4 GH.sub.z range. Usually the transistor chip is mounted on a microscript carrier that is suitable for wideband operation and is connected in the common base configuration. The carrier used could be constructed of beryllium oxide material. Base and emitter bonds having a minimum of parasitic reactance, excellent heat conduction and easy interconnection with the microscript carrier are used.
A further consideration in the design of transistor amplifier circuits is the existence of base to collector capacitance of the transistor and the necessity to compensate for this by the use of shunt tuning inductors. In practice, the shunt tuning inductor can be located directly on the carrier close to the chip and this will enhance the bandwidth capability of the transistor and also reduce losses and instabilities.
In Class A operation in a common base configuration usually two independent DC-bias supplies are needed, but it is common to overcome this limitation with an r-f bypass capacitance between base and ground which will effectively DC isolate the base from ground. The base-emitter bias is thus derivable from a resistive voltage divider. Special isolated-base carrier configuration can be designed that eliminates the bandwidth and stability problems which are usually encountered when using this method with packaged devices at high frequencies.
A constant consideration in design of a linear transistor microwave power amplifier is that additional tuning of the transistor chip amplifier circuit is needed after the transistor chip is mounted. In the past the tuning of the transistor chip device was usually accomplished by using a tunable inductor and a fixed capacitor. The tunable inductor was formed by a wire loop extending from the transistor chip to a fixed value blocking capacitor which is also mounted on the carrier. A problem which would arise when an attempt was made to adjust the inductance by changing the inductor loop size was that movement of the loop would tend to damage the transistor chip to which it was attached. Another previously known tuning mechanism consisted of constructing the inductor of two parts. One part of the tuning inductor extended from the transistor chip to an insulated standoff and the second part of the tuning inductor extended from the standoff to the blocking capacitor but this adjustment was limited in range. The object of the present invention is to provide an improved device for RF tuning and feedback adjustment of the transistor chip after the chip has been mounted on a carrier, the device being one that will increase the tuning control as well as not damaging the transistor as was previously the case.
The only known prior art would be the use of bendable capacitor tuning plates as are found in radio receivers and would be described in a communication engineering textbook.